In recent years, as a data communication amount increases in a communication field, a data rate has been increased in order to transmit a large amount of data on a single signal path. Through a communication path, not only an electrical signal but also a light signal may be transmitted. High-speed data has a problem that degradation such as, for example, an intersymbol interference occurs in cables, boards, and output devices.
Therefore, a pre-emphasis is performed in which an emphasis signal generating circuit (light emitting device driving circuit) generates an emphasis signal in which a part susceptible to degradation due to the signal intersymbol interference is enhanced in advance by considering deterioration of a signal, and outputs the emphasis signal to a transmission path.
As for an emphasis signal generating circuit that generates the emphasis signal, a finite impulse response (FIR) type emphasis signal generating circuit is known which branches and delays an input signal, and adds and subtracts the input signal and the branched and delayed input signal. A light emitting device such as a laser diode (LD) is driven by, for example, an emphasis signal (driving electrical signal) of which a rising/falling is emphasized, which is generated by the emphasis signal generating circuit to improve an output waveform (light signal).
However, in the related art, various proposals have been made as the light emitting device driving circuit (emphasis signal generating circuit) for driving the light emitting device such as the laser diode (LD).
Related technologies are disclosed in, for example, Japanese Patent Laid-Open Publication Nos. 2012-043933, 2015-139039, 2015-065687, 2012-256773, 2004-273631, and 2013-183147.